Urban agriculture is increasingly popular for social and economical benefits. However, edible crops grown in cities can be contaminated by airborne pollutants, thus leading to serious health risks. Therefore, we need a better understanding of contamination risks of urban cultivation to define safe practices. Here we study heavy metal risk in horticultural crops grown in urban gardens of Bologna, Italy. We investigated the effect of proximity to different pollution sources such as roads and railways, and the effect of the growing system used, that is soil versus soilless cultivation. We compared heavy metal concentration in urban and rural crops. We focused on surface deposition and tissue accumulation of pollutants during 3 years. Results show that in the city, crops near the road were polluted by heavy metals, with up to 160 mg per kilogram of dry weight for lettuce and 210 mg/kg for basil. The highest Cd accumulation of up to 1.2 mg/kg was found in rural tomato. Soilless planting systems enabled a reduction of heavy metal accumulation in plant tissue, of up to −71 % for rosemary leaves.

The influence of exposure to engineered nanoparticles (NPs) was studied in tomato plants, grown in a soil and peat mixture and irrigated with metal oxides (CeO2, Fe3O4, SnO2, TiO2) and metallic (Ag, Co, Ni) NPs. The morphological parameters of the tomato organs, the amount of component metals taken up by the tomato plants from NPs added to the soil and the nutrient content in different tomato organs were also investigated. The fate, transport and possible toxicity of different NPs and nutrients in tomato tissues from soils were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The tomato yield depended on the NPs: Fe3O4-NPs promoted the root growth, while SnO2-NP exposure reduced it (i.e. +152.6 and -63.1 % of dry matter, respectively). The NP component metal mainly accumulated in the tomato roots; however, plants treated with Ag-, Co- and Ni-NPs showed higher concentration of these elements in both above-ground and below-ground organs with respect to the untreated plants, in addition Ag-NPs also contaminated the fruits. Moreover, an imbalance of K translocation was detected in some plants exposed to Ag-, Co- and Fe3O4-NPs. The component metal concentration of soil rhizosphere polluted with NPs significantly increased compared to controls, and NPs were detected in the tissues of the tomato roots using electron microscopy (ESEM-EDS).

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Urban horticulture is increasingly popular for social and economic benefits. However, edible urban crops may be contaminated by airborne pollutants, thus leading to serious health risks. Therefore, a better understanding of contamination risks of urban cultivation is needed in order to define safe practices. In particular, whereas it is commonly accepted that the contamination of urban-grown food comes from airborne pollutants, little is known on a possible contamination by soils. Here, we studied trace metal risk in horticultural crops grown in an experimental urban allotment garden in Bologna, Italy. Seven experiments were conducted between June and November 2015 on tomato, sweet basil, onion, lettuce, kale, bulb fennel and radish. Treatments included two growing systems, soil and soilless, and two fertilization managements, mineral and organic. Trace metal concentrations were measured in soils, substrates and edible plant tissues. We identified preferentially translocated metals by partitioning analysis of tomato, sweet basil and kale. Results showed that crops grown in a soilless system have a lower metal content of −70 % for Cr, −61 % for Cu, −45 % for Cd and −81 % for Ni, compared with those grown in soil. This finding demonstrates that the major contamination risk in an urban area is unexpectedly related to soil pollution.

Salinity is a major constraint for plant growth in world areas exposed to salinization. Sorghum bicolor (L.) Moench is a species that has received attention for biomass production in saline areas thanks to drought and salinity tolerance. To improve the knowledge in the mechanisms of salt tolerance and sodium allocation to plant organs, a pot experiment was set up. The experimental design combined three levels of soil salinity (0, 3, and 6 dS m−1) with three levels of water salinity (0, 2–4, and 4–8 dS m−1) and two water regimes: no salt leaching (No SL) and salt leaching (SL). This latter regime was carried out with the same three water salinity levels and resulted in average +81% water supply. High soil salinity associated with high water salinity (HSS-HWS) affected plant growth and final dry weight (DW) to a greater extent in No SL (−87% DW) than SL (−42% DW). Additionally, HSS-HWS determined a stronger decrease in leaf water potential and relative water content under No SL than SL. HSS-HWS with No SL resulted in a higher Na bioaccumulation from soil to plant and in translocation from roots to stem and, finally, leaves, which are the most sensitive organ. Higher water availability (SL), although determining higher salt input when associated with HWS, limited Na bioaccumulation, prevented Na translocation to leaves, and enhanced selective absorption of Ca vs. Na. At plant level, higher Na accumulation was associated with lower Ca and Mg accumulation, especially in No SL. This indicates altered ion homeostasis and cation unbalance.